1. Field of the Invention
The present invention relates to devices for packaging selected items. More particularly, the present invention relates to devices for continuously packaging selected items in a controlled atmosphere enclosure. Further, the present invention relates particularly to devices for continuously packaging selected food items in a controlled atmosphere enclosure.
2. Description of the Related Art
It is known to package items, for example selected food items, in packages having a controlled atmosphere. Normally, this controlled atmosphere is a low oxygen atmosphere, with the oxygen replaced by an inert gas. Such controlled atmosphere enclosures or packages are necessary to insure adequate shelf life for many of the selected food items, for example. By eliminating the majority of oxygen from the package, the shelf life of the food item is greatly increased. Controlled atmosphere enclosures or packages are necessary for other items such as, for example, electronic components and moisture and oxygen sensitive materials. In certain applications this controlled atmosphere is preferably a high oxygen content atmosphere.
Normally, the controlled atmosphere within the package is obtained in one of two conventional ways. First, machines have been adapted to simply introduce the inert gas into the stationary package, with the inert gas partially displacing the ambient oxygen in the package. After the inert gas is introduced, the package is sealed. A teaching of this type may be found in U.S. Pat. No. 4,409,252 issued to Buschkens et al. for example. This method has generally proved unsatisfactory because it is extremely difficult to lower the oxygen content within the package to a desirable level, and it is extremely slow.
The second method of achieving a controlled atmosphere in the package has been by utilizing a vacuum in combination with a gas flush machine. In such a conventional machine, the package is placed in a vacuum chamber which creates a vacuum in the package. After the vacuum has been created in the package, the selected gas is introduced into the package, and the package is then sealed. Examples of teaching of this type include, for example. U.S. Pat. No. 4,009,552 issued to Schlachter, and U.S. Pat. No. 4,294,859 issued to Lundquist et al. However, all of these conventional vacuum gas flush devices utilize a vacuum chamber to perform these functions. In all of these devices, it is necessary for the package to stop for a period of time in the vacuum chamber. Thus, none of the conventional vacuum gas flush devices is capable of continually conveying a series of packages, with the controlled atmosphere introduced into the package and the package sealed without stopping the packages. Production using conventional devices is slow an therefore expensive. Some conventional vacuum gas flush devices, such as that disclosed in U.S. Pat. No. 4,058,953 issued to Sanborn, Jr. et al. and U.S. Pat. No. 4,791,775 issued to Raque et al., for example, also introduce a vacuum through one side of the package, while the selected gas in introduced through the opposite side of the package. However, these systems require a flexible container into which slits can be cut and then resealed after evacuation and modified atmosphere introduction.